In recent years, a great deal of interest has been shown in the provision of electrochromic displays having, for example, a digital or analog read out such as in commonly assigned U.S. Pat. No. 3,908,355 issued Sept. 30, 1975 in the name of Leo Wiesner and U.S. Pat. No. 3,987,433 issued Oct. 19, 1976 in the name of Richard Howard Kennedy.
Other prior art patents of interest includes U.S. Pat. No. 3,932,860 issued Jan. 13, 1976 to Sam G. Cohen, U.S. Pat. No. 3,881,311 issued May 6, 1975 to Tetsuro Hama et al, U.S. Pat. No. 3,797,225 issued Mar. 19, 1974 to Tetsuro Hama et al, U.S. Pat. No. 3,949,242 issued Apr. 6, 1976 to Masataka Hirasawa et al, U.S. Pat. No. 3,807,832 issued Apr. 30, 1974 to George Augustus Castellion and U.S. Pat. No. 3,839,857 issued Oct. 8, 1974 to Donald Joseph Berets et al. These prior art patents are merely typical of the art showing passive electro-optic display devices and other pertinent references may exist.
From the prior art, it is known to write selected segments by applying a voltage of one potential (usually having a negative polarity) with respect to a common electrode for a period to completely write the selected segments and then removing said potential from the written segments. Similarly, erasing of a segment was effected by applying a voltage of opposite polarity with respect to the common electrode for a period to completely erase the selected segments and thereafter removing said voltage.
Thus, the written and erased electrode-segments were open-circuited upon completion of each transition period, relying on the inherent memory or "persistent electrochromism" of the electrochromic layer to maintain its charge-potential and, therefore, its state of coloration and transparency, respectively.